I saw someone prefered using ODBC from PHP to access FM data, rather than PHPAPI.
I think if you don't need to call FM script from PHP, it may be good.
There are PHP examples in the Filemaker Server / Documenation folder.
It's a nice easy place to start and to get working example code.
As Carl says use the examples in the server documentaion folder. As well the CWP PDF resource is also helpful.
Here is what I can tell you from my experience, It is far faster than Web Direct as you are only sending and receiving the exact pieces of data you need. If your PHP web server has some sort of OPCache storing all the pre-compiled PHP you will benefit even more.
The only issue I had was an error related to externally stored containers when the containers were internal.
It is all fairly simple to use the PHP API if you have a good knowledge of PHP.
Jonathan Stark's book is an excellent reference:
Web Publishing with PHP and FileMaker 9
A complete listing of classes and methods for the FileMaker API for PHP
Brisbane ( Australia)
VTC.com has an excellent video course on the FileMaker PHP API. The first few chapters are free to view as I recall. It was well worth the investment IMO. Did a great job of explaining how all the parts and pieces work together, and the example files alone were worth the price of admission. I think in his video he was using FM 12 with one of the later big cat OS X versions.
There's a more advanced video in the resources section of this site.
It's probably NOT a good place for a beginner to start though, I wouldn't recommending starting fresh with any of the frameworks suggested there but if you are already familiar with those frameworks then I figured it may be worth pointing it out to you:
Todd Duell's book
FileMaker API for PHP 13
is much easier to read and follow along than the other books listed above. I've tried them all. http://www.formulationspro.com/pages/products/products_detail.php?id=109
HTML user interface is possibly a much broader topic that using PHP and FM, but I might recommend looking at jquery UI for a nice, cross platform compatible library to use. Certainly not the only option tho.
Hope this helps
I'm going to throw in my vote and agree with Jim Hoyt -- Todd Duell's book
FileMaker API for PHP 13
is as good as it gets. Great examples and sample code. Very well written and easy to follow. And Todd covers everything you need to get the job done !!!
what Mike Duncan said!
Knowing how to integrate PHP with those? The books and other resources are indispensable!